If you are flying domestically from Gimpo Airport, you can reach Gimpo Airport either by AREX, subway or bus. These pictures are taken when I was flying to Jeju Island from Gimpo Airport with T'Way Airlines. Further info on transportation is here.
This is from Gyeyang Station to Gimpo. As previously I was from Jakjeon
Station, I had to transfer from Seoul Metro to AREX from Gyeyang to Gimpo
You could see the grey line as AREX. It took me about 20 minutes
for 1,000 won using T-Money.
If you're coming from Seoul Station, take the rapid train from Seoul
to Gimpo. The rapid train will stop only at 3 stations (red dots) before
reaching Gimpo Airports. Time is 20 minutes for 1,100 won with T-Money.
Please check with the officer which platform is for rapid train to Gimpo
Airport before riding the train, if not you will take the normal train which
stops at every station.
Waiting for AREX at Gyeyang Station.
Inside AREX, not much difference from Seoul Metro.
After alighting the AREX, I saw this brand new cafe and from here
you can transit to Line 5 if you are heading to Seoul.
Take the elevator to B1.
Exit from AREX station.
Turn left to Domestic Terminal
or right for International Terminal or Line 5
Once you turn left, you will see this long escalator.
Once you reach the end, take the escalator to 2nd Floor
to check in your luggage and boarding.
The whole stretch is counters for checking in. T'Way Airlines
is the left end.
After check in, we head to 1st floor to board the flight.
Then we had a short bus ride to the flight which I thought
was so unnecessary but we had to.